In the manufacture of vinylidene chloride (1,1-dichloroethylene) by the dehydrohalogenation at elevated temperatures of 1,1,2-trichloroethane in the presence of caustic, the unsaturated vinylidene chloride product is very likely to polymerize either in the reactor or in the purification system thereafter because of conditions which are conducive to polymer formation in both places. Thus, it becomes necessary to employ some compound which will inhibit the polymerization.
Amines generally have been employed as stabilizers and storage inhibitors at ambient temperatures for chlorinated hydrocarbons, especially for inhibiting the polymerization reaction of the unsaturated chlorinated hydrocarbons such as vinyl chloride, vinylidene chloride, trichloroethylene and the like. Light and air are catalysts for the polymerization of such compounds and lower alkyl amines and aromatic amines have been claimed to protect vinylidene chloride in storage (U.S. Pat. No. 2,160,944). Isopropylamine is claimed in British patent 627,930 as an inhibitor for vinylidene chloride in the presence of air at elevated temperatures (65.degree. C).
Phenols have been employed as storage stabilizers for trichloroethylene and other chlorinated hydrocarbons either alone or in combination with substituted phenols and other compounds. Such stabilizers are disclosed in U.S. Pat. Nos. 3,230,175; 3,293,312 and 3,767,507.
Such compounds cannot be employed in the dehydrochlorination reactor, however, for, if they contact the caustic, they will react with it and be lost as inhibitors. Further, the phenolic compounds may even inhibit the dehydrohalogenation reaction. Thus, the usual way to employ phenolic inhibitors is to add them to the condenser immediately following the reactor. The inhibitor must also be carried over into the drying and finishing columns, or added thereto, in order to prevent polymerization there also. These inhibitors (phenolic compounds) will not pass overhead with the vinylidene chloride, but remain with the unreacted beta-trichloroethane. Before the unreacted starting material can be recycled to the reactor, it must be separated from such phenolic inhibitors for the reasons given heretofore.
Thus, it would be desirable to have an inhibitor which would not be deleterious to the reaction, nor be lost by reaction with caustic, which could be carried through the drying step to the distillation column and could be recycled to the reactor with the unreacted beta-trichloroethane.